See-through faces, but just in game and probably not because of normals?
This was actually my question, I managed to solve it.

The problem was, that there were some vertices, which haven't got any weight in the animation and therefore the game engine couldn't render their faces right.

I fixed it by editing more weight to this vertices.

The black area was the real face of the ape, for some reason you weren't able to see it even from backside.